Image display device having a transmissive panel and an optical isolator

ABSTRACT

A color management system for use with projection displays includes, for example, two or more analyzers positioned to receive light beams emitted from corresponding image assimilators, which each comprise a transmissive panel and a polarizing beamsplitter. Each analyzer is positioned to receive a light beam directly from an associated image assimilator before the light has passed through another optical element such as a light combiner. The analyzers are configured for producing filtered light outputs with improved contrast relative to the incoming light beams. These closely-coupled analyzers are able to remove substantially all of the noise before it has become indistinguishable, on the basis of polarization, from the light that comprises the desirable image. In an exemplary embodiment, an optical isolator is positioned to receive both a light output from a color management system and a reflection of the light output. The optical isolator is configured for isolating the light output from the reflection.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Nonprovisional patentapplication Ser. No. 10/431,890 filed May 8, 2003, now U.S. Pat. No.6,899,432, which claims benefit of priority from U.S. Provisional PatentApplication Ser. No. 60/378,879 filed May 8, 2002, which is herebyincorporated by reference. This application is also acontinuation-in-part of, and claims benefit of priority from U.S.Nonprovisional Patent Application Ser. No. 10/310,383, filed Dec. 5,2002, now U.S. Pat. No. 6,857,747, which is also a continuation-in-partof, and claims benefit of priority from U.S. Nonprovisional patentapplication Ser. No. 10/213,505, filed Aug. 6, 2002, now U.S. Pat. No.6,851,812, which claims benefit of priority from U.S. Provisional PatentApplication Ser. No. 60/310,077 filed Aug. 6, 2001, all of which arehereby incorporated by reference.

FIELD OF INVENTION

The present invention relates generally to color management systems forprojection displays, and more specifically to systems and methods forincorporating a transmissive panel and/or optical isolator into a systemfor separating input illumination into separate color channels,superimposing spatial information on each of the separate channels,eliminating unwanted noise, and recombining the separate color channelsto facilitate projection of a high-contrast, full color image.

BACKGROUND OF THE INVENTION

In conjunction with a projection display, it is desirable to employ acolor management system, and it is further desirable that such colormanagement system facilitate the production of a high contrast imagewhile accommodating a relatively high level of illuminating flux andproviding for efficient packaging. Unfortunately, currently existingcolor management systems are capable of achieving increased contrast atpractical levels of illuminating flux only by employing highlyspecialized materials, resulting in unreasonable increases in cost.

A color management system typically functions by first separating inputlight (e.g., white light) into a plurality of color channels traversingthe visible spectrum (e.g. red, green and blue), then using the separatecolor channels to illuminate a plurality of corresponding microdisplays(e.g., LCoS microdisplays) and recombining the color channels to producean output light (e.g., white light). Where it is desired to project animage in conjunction with the output light beam, spatial information maybe superimposed into each of the color channels by the microdisplaysprior to recombination. As a result, a full color image may be projectedin conjunction with the output light beam. As used herein, the terms“microdisplay,” “panel,” “display,” “display panel,” and “light valve”refer to a mechanism configured for receiving an incipient light beam,imparting spatial information in the light beam, and emitting a modifiedlight beam comprising the incipient light beam and the spatialinformation. An example of such a microdisplay is model number DILASX-070 manufactured by the JVC company of Japan.

It should be noted that a microdisplay may be configured as asubstantially reflective display panel or as a substantiallytransmissive display panel. A substantially reflective display panel isconfigured to emit a modified light beam toward a direction that issubstantially toward the direction from which the incipient light beamcame (i.e., to retroreflect). A substantially transmissive display panelis configured to emit a modified light beam toward a direction that issubstantially similar to the direction in which the incipient light beamtravels (i.e., to transmit a modified light beam through the panel). Forexample, a reflective panel may be configured to receive an incipientlight beam traveling in a first direction, to impart spatial informationupon the light beam, and to emit a modified light beam toward thedirection from where the incipient light beam originated (i.e.,reflected 180 degrees from the direction of the incipient light beam).Alternatively a transmissive panel may be configured to receive anincipient light beam, to impart spatial information in the light beam,and to emit a modified light beam in substantially the same direction asthat in which the incipient light beam travels.

Prior art color management systems have thus far not sufficiently provento be able to produce high contrast images at low cost withoutcompromising their ability to maintain reasonable quantities ofilluminating flux or to be packaged efficiently. This is due, in part,to image noise caused by optical characteristics that are inherent inall real optical elements. This is also due to the inability ofcurrently existing color management systems to effectively separate andremove such noise from the light beam before it is projected to adisplay.

For example, many prior art color management systems use solid“cube-type” polarizing beamsplitters for color separation andrecombination. These polarizing beamsplitters are otherwise referred toas MacNeille prisms or cube polarizing beamsplitters. “Cube type”polarizing beamsplitters are inherently susceptible to thermal gradientsthat typically arise at high flux levels, often causing stressbirefringence which results in depolarization of the light and a loss ofcontrast. As a result, where high contrast images are desired, it hasbeen necessary to use costly high-index, low-birefringence glass.Although this solution has proven effective to reduce birefringence atlow levels of flux, it is expensive and exhibits reduced effectivenessat eliminating thermally induced birefringence at high flux levels(e.g., greater than approximately 500 lumens).

For example, FIG. 1 illustrates a prior art color management system 110,commonly known as the ColorQuad™ from Colorlink, in which four cubepolarizing beamsplitters and five color selective retardation elementsare used to provide color separation and recombination. In accordancewith this system, the input cubic polarizing beamsplitter receives aninput light beam 120 and separates it into three components, a greencomponent 121, a blue component 122, and a red component 123. The redcomponent 123 receives spatial information from a reflective red panel133; the blue component 122 receives spatial information from areflective blue panel 132; and the green component 121 receives spatialinformation from a reflective green panel 131. Finally, the output cubicpolarizing beamsplitter recombines the red component 123 and bluecomponent 122 with green component 121 to form a full color image 140,which may be received by a projection lens or other optical elementsdepending on the purpose of the system.

It should be noted that at high levels of light flux, cubic polarizingbeamsplitter 110 typically becomes thermally loaded and necessarilydistorts physically, causing stress birefringence, which often resultsin depolarization of the light and a decrease in contrast. Further, inaddition to receiving spatial information from the red, green and bluepanels in the cubic polarizing beamsplitter 110, the red, green, andblue light components also typically receive undesirable spatialinformation as a result of birefringence in the materials of the opticalcomponents in the red, green, and blue light paths. This undesirablespatial information tends to further decrease the contrast of the image.

In an attempt to reduce the adverse effects of the use of cubepolarizing beamsplitters, various attempts have been made to implementplate polarizing beamsplitters in place of cube configurations in colormanagement systems. However, these attempts have often given rise toother optical aberrations associated with the plate polarizingbeamsplitters, such as astigmatism. Thus, it is well understood thatmost if not all optical elements used in today's color managementsystems contribute noise to, and/or otherwise corrupt, any light beampassing through, or affected by, the optical element. It should be notedthat, as used herein, the terms “noise” and/or “corrupt[ion of a] lightbeam” refer to optical effects associated with, and/or comprising, forexample, scatter, polarization rotation (e.g., non-homogenouslypolarized light emitted from a polarizing beamsplitter that may comprisecomponents having undesirably rotated polarization orientations),material birefringence, and or other undesirable characteristicsassociated with geometries and or coatings of optical elements, and thelike.

Accordingly, many color management systems also include optical filters,such as analyzers or polarizers that are configured to attempt toeliminate most or all of such noise from the light beam so that asubstantial portion of the contrast of the image might be restored.These filters may attempt to eliminate such noise, for example, byseparating light according to its polarization. This is made possible bythe fact that the desirable light components of the light beam may beoriented with a first polarization while the noise may be orienteddifferently or otherwise not substantially polarized.

Unfortunately, however, as a light beam passes through, or is affectedby, an optical element, the polarization of the light tends to bedisturbed. Thus, a portion of the noise often becomes indistinguishable,on the basis of polarization at least, from the light that comprises thedesirable image. Accordingly, the opportunity to fully and effectivelyeliminate noise from the light beam on the basis of polarizationdiminishes as the tainted light beam passes through, or is affected by,each successive optical element. Nevertheless, in prior art systems, theadditional light constituents are not removed until after the corruptedlight beam has passed through, or has been affected by, additionaloptical elements, such as a light recombiner, a prism, and/or the like.

In addition to these and other difficulties, prior art systems are oftensusceptible to the effects of stray light which may undesirably reachthe optical components and inadvertently be combined with, or otherwisecorrupt, the desirable image imparted by the panels onto the modifiedlight beam. For example in many prior art systems, wherein the outputlight beam is transmitted to a projection lens or another opticalcomponent, a portion of such light may unfortunately be reflected by thecomponent and transmitted back (i.e., retroreflected) toward andreceived by other system components. The reflected light, then, may beundesirably recombined with the desirable light to produce a compositelight beam containing both the desirable image and, for example, a ghostof the desirable image. Accordingly, the combined ghost-bearing imagemay be undesirably transmitted to the display.

In addition, prior art color management systems employing transmissivepanels frequently encounter extreme thermal conditions in the opticalcomponents that are positioned downstream of the transmissive panel.This common problem is caused by the need for waste light to be rejectedfrom the modified light beam, and may occur where the panel fails toperform the elimination of such waste light. Such situations,unfortunately, are much more common with transmissive panels than withreflective panels. More particularly, in typical color managementsystems, the incipient light beam which is received by a panel bears afixed intensity or brightness. The panel, then, after receiving theincipient light beam, imparts spatial information on (i.e., modifies)the light beam by modulating the intensity of light at each of a largenumber of discrete locations (e.g., pixels). Typically, reflective panelsystems accomplish this by reflecting (i.e., emit) only the lightcomprising the desirable image, by absorbing the waste light andemitting the generated heat. Transmissive panels, on the other hand,typically transmit substantially all of the incipient light theyreceive, but impart spatial information by spatially modifying selectedproperties (e.g., polarization) of the light beam. Accordingly, systemsemploying transmissive panels frequently must rely upon a downstreamoptical component to reject the waste light (and heat) based on thespatially modified properties (e.g., polarization). Accordingly, as thewaste light is rejected, heat is generated. The requirement that aparticular component be configured to accommodate rejection of largequantities of light often imposes difficult design constraints on thoseoptical components.

Accordingly, it would be advantageous to have a color management systemthat could be used in high flux projection systems while simultaneouslyfunctioning in a wide range of thermal environments with reducedbirefringence sensitivity and improved durability while producing ahigh-contrast image. It would further be advantageous to have a colormanagement system that could achieve these objectives without requiringcostly, high index, low birefringence glass or a particularsusceptibility to optical aberrations produced by polarizingbeamsplitters in plate configurations. It would further be advantageousto have a color management system that could achieve these objectiveswhile eliminating or reducing ghosts or other undesirable images causedby stray light. It would further be advantageous to have a colormanagement system that could achieve these objectives in transmissivepanel systems while relieving the extreme temperature environmentdifficulties associated with such transmissive panels.

SUMMARY OF THE INVENTION

The methods and apparatus of the present invention address many of theshortcomings of the prior art. In accordance with various aspects of thepresent invention, improved methods and apparatus facilitate colormanagement for projection display systems. The effective colormanagement of the present invention is suitable for use in high fluxprojection systems with improved contrast, birefringence sensitivity,and durability, while significantly reducing cost. In addition, thepresent invention provides color management suitable for use in adversethermal environments without requiring costly, high index, lowbirefringence glass.

In accordance with an exemplary embodiment of the present invention, acolor management system includes two or more analyzers positioned toreceive light beams as they are emitted from the panels of a colormanagement system. The analyzers are positioned to receive the lightbeams directly from the image assimilators before the light has passedthrough another optical element such as, for example, a light combiner.The analyzers are configured for producing filtered light outputs withimproved contrast relative to the incoming light beams. By positioningthe analyzers to receive the light beams directly from the imageassimilators, i.e., prior to passage through other optical elements, theanalyzers are able to remove substantially all of the noise before thenoise has become indistinguishable, on the basis of polarization, fromthe light that comprises the desirable image. Accordingly, thisembodiment produces images having dramatically improved levels ofcontrast and dark state uniformity relative to prior art systems.

In accordance with another exemplary embodiment of the presentinvention, each analyzer may also include an optical retarder element,such as a half-wave retarder or a quarter-wave retarder. Where thefilter comprises an optical retarder element, the retarder element maybe configured to selectively modify the polarization of the lightemerging from the image assimilator so that the emerging light issubstantially linearly polarized and further so that the polarizationaxis for each color band is substantially the same as that of each othercolor band. It should be noted that such optical retarder elements maybe selected to exhibit a specific optical retardence, for example,between 15 nanometers and 350 nanometers of optical retardence,depending upon the extent to which rotation is desired to match theresidual retardence in the image assimilator, e.g., to substantiallycompensate for the optical retardence of the panel. Optionally,depending on the characteristics of the optical retarder element, theanalyzer may be configured to remove light of a predeterminedwavelength, or band of wavelengths, from the light output.

In an exemplary embodiment, a color management system comprises a singlepanel, or may comprise two or more panels, wherein each panel receivesand emits a separate light component. In accordance with thisembodiment, the separate light components may have originated from alight source, from which a light beam was received by one or more lightseparators. Each such light separator is positioned to receive a lightinput comprising two or more components, and each such light separatoris configured for separating the components from one another and foremitting two or more light beams, each comprising one or more of thecomponents.

In an exemplary embodiment, a color management system may furthercomprise a third panel for receiving and emitting a third lightcomponent. In this embodiment, an additional light separator ispositioned to receive one or more of the light beams from a first lightseparator, and the additional light separator is configured to furtherseparate the light emitted by the first light separator into twoadditional components. Each light separator may comprise a dichroicbeamsplitter, a dichroic prism coupled with an optical retarder, a platedichroic beamsplitter, and/or a polarizing beamsplitter, which mayfurther comprise a wire grid polarizer. Each light separator may beconfigured for producing a red light output, a green light output, ablue light output, or a cyan light output comprising green light andblue light.

In an exemplary embodiment, a color management system may comprise oneor more image assimilator, each being associated with a light component.Each such image assimilator may comprise a reflective spatial lightmodulator configured to modify the polarization of the incoming lightbeam in a predetermined manner and to superimpose spatial information onthe light beam so as to produce a light beam that comprises spatialinformation. Each such reflective image assimilator is configured forsubstantially transmitting an incoming light beam to be received by areflective display panel, to receive a modified light beam from thereflective display panel, and to emit the modified light beam to bereceived directly by an analyzer. In such a configuration, as thereflective panel produces a modified light beam comprising spatialinformation, the panel also filters and rejects waste light.

Alternatively, each image assimilator may comprise a transmissivespatial light modulator that may similarly be configured to modify thepolarization of the incoming light beam in a predetermined manner and tosuperimpose spatial information on the light beam so as to produce alight beam that comprises spatial information. Each such transmissiveimage assimilator is configured for receiving an incoming light beam,superimposing spatial information on the light beam, optionallyrejecting or filtering waste light to produce a modified light beam, andemitting the modified light beam to be received directly by an analyzer.

In addition to a spatial light modulator, each image assimilator maycomprise a plate dichroic beamsplitter, a dichroic prism coupled with anoptical retarder, and/or a polarizing beamsplitter which may furthercomprise a wire grid polarizer. As discussed briefly above, in areflective panel, the panel may be configured to reject waste light. Ina transmissive panel configuration, however, the panel may not beconfigured to filter and reject the waste light, but may be configuredto modify only its polarization. Accordingly, image assimilatorscomprising such non-filtering transmissive panels may also comprise awaste light separator. For example, in an exemplary embodiment, thewaste light separator may comprise a wire grid polarizer positioned toreceive the modulated light beam emitted from the transmissive displaypanel and to selectively reject the undesirable waste light on the basisof polarization.

In an exemplary embodiment, a color management system also includes alight combiner positioned to receive the filtered light beams emittedfrom the analyzers, which receive light directly from the imageassimilators. The light combiner is configured to combine the filteredlight outputs to produce a single filtered light output. The lightcombiner may comprise a dichroic beamsplitter or an x-prism. If thelight combiner is an x-prism, it may include one or more dichroicfilters and may also include a polarizing beamsplitter. As discussedbriefly above, in color management systems where the image assimilatorscomprise transmissive panels but fail to completely or effectivelyseparate and reject waste light prior to transmission to downstreamcomponents, such as the analyzer or the light combiner, such componentsmust be configured to accommodate increased thermal loading associatedwith the additional transmitted waste light. In transmissive panelsystems wherein the image assimilators comprise an effective means forseparating and rejecting waste light, such as a polarizing beamsplitter,downstream components, such as the analyzer or the light combiner, maybe configured to accommodate decreased thermal loading.

The color management system may also include a projection lens forprojecting an output light beam containing spatial information forprojecting an image. In an exemplary embodiment, the color managementsystem may include an optical isolator positioned to isolate any lightthat may be reflected by the projection lens or another opticalcomponent and to prevent such stray light from being received by thelight combiner or another optical component of the system and beingrecombined with the modified light beam. Accordingly, the opticalisolator may be effective in eliminating or reducing unwanted ghostimages and other undesirable effects of stray light.

In accordance with an exemplary embodiment of the present invention amethod for facilitating color management for a projection system isprovided comprising the steps of receiving two or more input light beamshaving spatial information and noise directly from associated imageassimilators, separating the noise from the spatial information in eachof the light beams, and emitting filtered light outputs comprising thespatial information, whereby the output light beams have an improvedcontrast relative to the input light beams. In accordance with anexemplary embodiment of the present invention a method for facilitatingcolor management for a projection system may comprise rejecting wastelight from a modified light beam before filtering said light beam toproduce a light beam having improved contrast relative to the modifiedlight beam.

As used herein, the term “component” refers to a portion of a lighttransmission. For example, where a light transmission contains light ofvarious wavelengths in the visible spectrum (e.g., blue, red, andgreen), the light transmission may be separated into a plurality ofcomponents, each corresponding to a range of wavelengths (i.e., colorbands), such as blue, red, or green, in the visible spectrum. As afurther example, a light transmission may comprise polarized lightoriented in one or more planes.

Accordingly, the use of closely-coupled analyzers positioned to receivelight beams directly from associated image assimilators enables thecolor management system to effectively eliminate a substantial portionof noise imparted on the light beam by each of the image assimilatorsand to produce output beams having superior contrast relative to theprior art. Moreover, the present invention may employ both polarizationdependent elements and dichroic elements to split an input light into aplurality of color bands upon which spatial information may besuperimposed by a corresponding plurality of microdisplays, the modifiedcolor bands being recombined to produce a high-contrast, full colorprojected image.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned objects and features of the present invention can bemore clearly understood from the following detailed descriptionconsidered in conjunction with the following drawings, in which likenumerals represent like elements and in which:

FIG. 1 illustrates a prior art color management system;

FIG. 2 illustrates a color management system in accordance with anexemplary embodiment of the present invention;

FIG. 3 is a flow chart illustrating an exemplary method in accordancewith the present invention;

FIG. 4 illustrates a color management system in accordance with anexemplary embodiment of the present invention; and

FIG. 5 illustrates a color management system in accordance with anexemplary embodiment of the present invention.

DETAILED DESCRIPTION

The present invention may be described herein in terms of variousfunctional elements and/or various processing steps. It should beappreciated that such functional elements may be realized by any numberof software, hardware, electrical, optical and/or structural elementsconfigured to perform the specified functions. For example, the presentinvention may employ various optical and/or digital electrical elements,whose values may be suitably configured for various intended purposes.In addition, the present invention may be practiced in any opticalapplication. However, for purposes of illustration only, exemplaryembodiments of the present invention will be described herein inconnection with projection displays. Further, it should be noted thatwhile various elements may be suitably coupled or connected to otherelements within exemplary optical systems, such connections andcouplings can be realized by direct connection between elements, or byconnection through other elements and devices located thereinbetween.

As discussed above, prior art color management systems suffer fromshortcomings such as limitation in light intensity, high cost, poorimage contrast, excessive birefringence sensitivity, and lack ofdurability. Prior art attempts to overcome these shortcomings haveinvolved the use of costly high-index, low-birefringence glass. Yet,despite the use of these expensive materials, poor image contrast, andthermally induced birefringence remain problems at light intensitylevels greater than approximately 500 lumens.

In accordance with various aspects of the present invention, an improvedcolor management system is provided that improves image contrast andfacilitates color management suitable for use in adverse thermalenvironments without requiring costly, high index, low birefringenceglass. The invention includes any suitable system or method for closelycoupling analyzers to image assimilators. The invention also includesany suitable system or method for the analyzers to receive light beamsdirectly from the image assimilators, and in certain embodiments,analyzers receiving two or more light beams directly from imageassimilators. In accordance with an exemplary embodiment of the presentinvention, input illumination light is split into a plurality ofdifferent color bands and then recombined after superimposition ofspatial information by a corresponding plurality of microdisplays andreduction of noise as provided by corresponding filters, therebyproducing a substantially full-color, high-contrast image. As a result,effective color management of the present invention is suitable for usein high lumen projection systems with reduced cost, improved contrast,reduced birefringence sensitivity, improved dark state uniformity, andimproved durability. In addition, the present invention provides colormanagement suitable for use in adverse thermal environments withoutrequiring costly, high index, low birefringence glass.

In one embodiment, with reference to FIG. 2, an exemplary colormanagement system 200 includes a light separator 220, a first imageassimilator 230, a second image assimilator 240, a first analyzer 235, asecond analyzer 245, and a light combiner 250. In accordance with thisembodiment, light separator 220 receives a light beam 210 from a source,separates the light beam 210 into two or more components 212, 214, 216,and emits two or more light beams 222, 224, each comprising one or moreof the components. For example, as shown in FIG. 2, light separator 220is positioned to receive a light input 210 comprising a first componentand a second component. Light separator 220 is configured for separatingsaid first component from said second component and emitting a firstlight beam 222 comprising said first component 212 and a second lightbeam 224 comprising said second component 214 and a third component 216.It should be noted that light separator 220 may comprise a polarizingbeamsplitter configured for separating light oriented in a first planefrom light oriented in a second plane and emitting a first light beam222 comprising light oriented in the first plane 212 and a second lightbeam 224 comprising light oriented in the second plane 214. It should benoted that light separator 220 may comprise a dichroic mirror, adichroic beamsplitter, a dichroic prism coupled with an opticalretarder, a plate dichroic beamsplitter, or a polarizing beamsplitter,which may further comprise a wire grid polarizer. Light separator 220may be configured for producing a red light output, a green lightoutput, a blue light output, and/or a cyan light output comprising greenlight and blue light. As shown in FIG. 2, light separator 220 is adichroic plate beamsplitter configured to receive a modulated inputlight beam 210 and to emit two output light beams 222, 224. In oneembodiment, first output light beam 222 comprises a red component 212and second output light beam 224 comprises a blue component 214 and agreen component 216.

It should be noted that light separator 220 may also be configured forproducing light where color images are generated by temporallymodulating the color of the light into separate spectral bands, whichcan consist of red, green, and blue, or any other combination that couldbe recombined to produce a desired output, such as a white light output.As shown in FIG. 2, light separator 220 is a polarizing platebeamsplitter configured to receive a modulated input light beam 210 andto emit two output light beams 222, 224. First output light beam 222comprises a polarized light component 212. Second output light beam 224comprises a polarized light component 214 which is substantiallyorthogonal to the polarized light component 212 of the first light beam222.

It should be noted that, in general, a polarizing beam splitter 220 is adevice configured to separate an incipient beam of light 210 into twoemergent linear polarized beams of light 222, 224. As such, polarizingbeamsplitter 220 may comprise a dichroic mirror having a coatingconfigured to separate light 210 into components of different colors212, 214. For example a typical coating may be a thin film dielectriccoating. In another embodiment, polarizing beamsplitter 220 may be adielectric beamsplitter having a coating configured to separate lightinto different components 212, 214 based upon, for example, color orpolarization.

In accordance with the invention, polarizing beamsplitter 220 isconfigured for separating polarized light oriented in a first plane frompolarized light oriented in a second plane. In an exemplary embodiment,polarizing beamsplitter 220 may be configured to emit in a firstdirection the polarized light oriented in the first plane 212 and toemit in a second direction the polarized light oriented in a secondplane 214, wherein the second direction is substantially orthogonal tothe first direction. In another exemplary embodiment, polarizingbeamsplitter 220 may be configured, as shown in FIG. 2, to substantiallytransmit the polarized light oriented in the second plane 214 and tosubstantially reflect the polarized light oriented in the first plane212.

In another embodiment, polarizing beamsplitter 220 may be configured tosubstantially reflect the polarized light oriented in the second planeand to substantially transmit the polarized light oriented in the firstplane. In accordance with this embodiment, a plurality of fold mirrorsmay be employed to direct the various light beams between the elementsof the color management system. As used herein, a fold mirror refers toany reflective surface capable of reflecting light. For example, a foldmirror may be an aluminized mirror or an enhanced silver mirror, such asthe Siflex mirror produced by Unaxis company of Liechtenstein.Polarizing beamsplitter 220 may comprise a pair of polarizingbeamsplitters having their active surfaces facing substantially awayfrom one another, or a single polarizing beamsplitter element withactive surfaces on both sides.

With further reference to FIG. 2, first image assimilator 230, whichcomprises first polarizing beamsplitter 232 and first microdisplay 234,is positioned to receive first output light beam 222. A second imageassimilator 240, which comprises second polarizing beamsplitter 242 andsecond microdisplay 244, is positioned to receive second output lightbeam 224. Each such image assimilator 230, 240 may comprise a reflectivespatial light modulator 234, 244 configured to modify the polarizationof the incoming light beam in a predetermined manner and to superimposespatial information on the light beam so as to produce a light beam thatcomprises spatial information. Each such image assimilator 230, 240 isconfigured for substantially transmitting an incoming light beam to bereceived by a display panel 234, 244, for receiving a modified lightbeam from the display panel, and for emitting the modified light beam236, 246 to be received directly by an analyzer 235, 245. Each imageassimilator 230, 240 may comprise a plate dichroic beamsplitter, adichroic prism coupled with or without an optical retarder, or apolarizing beamsplitter which may further comprise a wire gridpolarizer.

In accordance with this exemplary embodiment, first image assimilator230 receives a first output light beam 222, rotates its polarizationorientation, imparts first spatial information on it, and emits a firstmodified light beam 236 comprising first spatial information and noise.Second image assimilator 240 receives second output light beam 224,rotates its polarization orientation, imparts second spatial informationon it, and emits a second modified light beam 246 comprising secondspatial information and noise. In accordance with this embodiment, firstand second spatial information comprise polarized light.

In an exemplary embodiment, image assimilator 230, 240 may comprise adichroic prism. In an alternative embodiment, image assimilator 230, 240may be a substantially equal path length prism. In another exemplaryembodiment, image assimilator 230, 240 may comprise a polarizing filterfor producing a differentiated light output comprising the secondcomponent 214 and the third component 216, where the orientation of thesecond component 214 is rotated to be orthogonal to the orientation ofthe third component 216. In accordance with this alternative embodiment,image assimilator 230, 240 further comprises a second polarizingbeamsplitter positioned to receive from the polarizing filter thedifferentiated light output. This second polarizing beamsplitter isconfigured for separating the second component 214 from the thirdcomponent 216 before substantially transmitting the second component tobe received by the second microdisplay and before substantiallytransmitting the third component to be received by a third microdisplay.

Accordingly, in an exemplary embodiment, the contrast of the image maybe enhanced by such an analyzer 235, 245 positioned to receive themodified light outputs from image assimilator 230, 240 and to furthermodify the light to produce polarized light oriented in a single plane(i.e., substantially linearly polarized light) which may be accomplishedby rotating the polarization axis of one or more of the light beams. Inyet another exemplary embodiment, the analyzer 235, 245 may beconfigured for removing light of a predetermined wavelength from thelight beam, depending on the characteristics of the filters (i.e., thecolor selective retardation elements).

As used herein, the terms “filter” and “analyzer” refer to opticalfilters, and combinations of optical elements, configured todiscriminate (i.e., block, permit to pass, and/or alter the polarizationproperties of light flux based on physical characteristics of the light,such as wavelength, orientation, polarization, flash and/or field rate)and may be constructed using any technique known in the art such as, forexample, embedding an optically active material such as a spectrallysensitive optical retardation film in or on an otherwise transparentsubstrate or placing a plurality of very thin wires in parallelorientation to one another leaving thin gaps through which light maypass to produce polarized light. Examples of filters configured fordiscriminating light based upon its physical characteristics includedichroic plates manufactured by OCLI of Santa Rosa, Calif. and Unaxis ofLiechtenstein; ColorSelect filters manufactured by ColorLink of Boulder,Colo.; absorptive sheet polarizers manufactured by Polaroid, and ProFluxpolarizers and polarizing beamsplitters manufactured by Moxtek of OremUtah.

With further reference to FIG. 2, in an exemplary embodiment, firstanalyzer 235 is positioned to receive first modified light output 236directly from first image assimilator 230 and is configured to separatefirst spatial information from noise based on polarization. Inaccordance with this embodiment, first analyzer 235 is configured tosubstantially transmit first spatial information and to prevent orminimize transmission of noise, which comprises substantiallynon-polarized light or polarized light that is not oriented in the samemanner as the desired spatial information. It should be noted that firstanalyzer 235 may comprise a polarizer and may be configured to absorblight of a predetermined polarization (e.g., an absorptive polarizersuch as a stretched polymer polarizer), may be configured to reflectlight of a predetermined polarization (e.g., a reflective polarizer suchas a dichroic or wire grid polarizer), or may be configured to absorblight of a first polarization and to reflect light of a distinct secondpolarization (e.g., a hybrid polarizer). It should also be noted thatfirst analyzer 235 may also comprise a color filter such as a dichroicfilter or a bulk absorptive filter.

Similarly, second analyzer 245 is positioned to receive second modifiedlight output 246 directly from second image assimilator 240 and isconfigured to substantially separate second spatial information fromnoise based on polarization. As with first analyzer 235, it should alsobe noted that second analyzer 245 may comprise a polarizer and may beconfigured to absorb light of a predetermined polarization (e.g., anabsorptive polarizer such as a stretched polymer polarizer), may beconfigured to reflect light of a predetermined polarization (e.g., areflective polarizer such as a dichroic or wire grid polarizer), or maybe configured to absorb light of a first polarization and to reflectlight of a distinct second polarization (e.g., a hybrid polarizer). Itshould also be noted that second analyzer 245 may also comprise a colorfilter such as a dichroic filter or a bulk absorptive filter.

Also in accordance with this embodiment, second analyzer 245 isconfigured to substantially transmit second spatial information and toprevent or minimize transmission of noise, which, again, comprisessubstantially non-polarized light or polarized light that is notoriented in the same manner as the desired spatial information. Becausefirst analyzer 235 and second analyzer 245 are positioned to receivefirst modified light output 236 and second modified light output 246directly from first and second image assimilators 230, 240, prior tomodification by any other optical elements, first and second analyzers235, 245 are capable of eliminating or reducing or minimizingsubstantially all of the noise imparted by image assimilator 230, 240.

It should be noted that the analyzers 235, 245 are positioned to receivethe light beams directly from the image assimilators 230, 240 before thelight has passed through another optical element such as a lightcombiner 250. It should also be noted that analyzers 235, 245 aregenerally configured for producing filtered light outputs with improvedcontrast relative to the incoming light beams. By positioning theanalyzers 235, 245 to receive the light beams directly from the imageassimilators 230, 240, i.e., prior to passage through or modification byoptical elements other than those comprised by the image assimilators,the analyzers 235, 245 are able to remove substantially all of the noisebefore the noise becomes indistinguishable, on the basis ofpolarization, from the light that comprises the desirable image.Accordingly, this embodiment produces images having dramaticallyimproved levels of contrast relative to prior art systems.

In accordance with another exemplary embodiment of the presentinvention, each analyzer 235, 245 may also include an optical retarderelement, such as a half-wave retarder or a quarter-wave retarder. Wherethe filter comprises an optical retarder element, the retarder elementmay be configured to selectively modify the polarization of the lightemerging from the image assimilator so that the emerging light issubstantially linearly polarized and further so that the polarizationaxis for each color band is substantially the same as that of each othercolor band. As mentioned above, it should be noted that such filters maybe selected to exhibit a specific optical retardence, for example,between 15 nanometers and 350 nanometers of optical retardence,depending upon the extent to which rotation is desired to match theresidual retardence in the image assimilator, e.g., to substantiallycompensate for the optical retardence of the panel. Optionally,depending on the characteristics of the optical retarder element, theanalyzer 235, 245 may remove light of a predetermined wavelength, orband of wavelengths, from the light beam 236, 246.

In an exemplary embodiment, a color management system also includes alight combiner 250 positioned to receive the filtered light beams 237,247 emitted from the analyzers 235, 245. The light combiner 250 isconfigured to substantially combine the filtered light beams 237, 247 toproduce a single filtered light output 255. For example, as shown inFIG. 2, in an exemplary embodiment, the invention also includes a lightcombiner 250 that forms a comprehensive light output 255 from theindividual light outputs 237, 247. In an exemplary embodiment, the lightcombiner 250 comprises a polarizing beamsplitter, which may be the sameelement, and serve the substantially same function, as the lightseparator 220. The light combiner 250 may comprise a dichroicbeamsplitter or an x-prism. Where the light combiner 250 is an x-prism,it may include one or more dichroic filters and may also include apolarizing beamsplitter. It should be noted that where light combiner250 comprises an x-prism, the x-prism may be optimized for operationunder any one of a variety of polarization orientations. For example, anx-prism may be optimized to operate under s-s-s polarization, p-p-ppolarization, s-p-s polarization, or p-s-p polarization. Further, wherex-prism is optimized under p-s-p polarization, it may be configured toisolate and/or recombine light transmissions that comprise substantiallyred, green and blue components.

It should be noted that an x-prism is an optical element having twoplanes that lie substantially orthogonal to one another. In an exemplaryx-prism, a first plane is a dichroic filter configured to substantiallytransmit light having a first wavelength and to substantially reflectlight having a second wavelength. In such an exemplary x-prism, a secondplane, lying substantially orthogonal to the first plane, has a dichroicfilter configured to substantially reflect light having the firstwavelength and to substantially transmit light having the secondwavelength. In another exemplary x-prism, a first plane is a dichroicfilter configured to substantially transmit light having a firstwavelength and to substantially reflect light having a secondwavelength. In this exemplary x-prism, a second plane, lyingsubstantially orthogonal to the first plane, has a polarizingbeamsplitter configured to substantially reflect light oriented with afirst polarization and to substantially transmit light oriented with asecond polarization.

In an exemplary embodiment, such as the embodiment illustrated in FIG.2, wherein the first output light beam 222 is directed substantiallyperpendicular to the second output light beam 224, first polarizingbeamsplitter 232 and second polarizing beamsplitter 242 may comprise thesame polarizing beamsplitter oriented so as to receive both the firstoutput light beam 222 and the second output light beam 224 at asubstantially 45 degree angle from the surface of the polarizingbeamsplitter 232, 242. In accordance with this embodiment, polarizingbeamsplitter 232, 242 is configured to substantially transmit firstoutput light beam 222 to be received by first microdisplay 234 and tosubstantially transmit second output light beam 224 to be received bysecond microdisplay 244. Polarizing beamsplitter 232, 242 is alsopositioned to receive modified first and second light beams 236, 246 ata substantially 45 degree angle. Because the polarization of themodified light beams 236, 246 are rotated from the orientation of lightbeams 222, 224, however, polarizing beamsplitter 232, 242 is configuredto substantially reflect the modified light beams 236, 246. Therefore,in accordance with this embodiment, both of the modified light beams236, 246 may be directed directly toward light combiner 250. The abilityto use a single polarizing beamsplitter 232, 242 and to direct themodified light beams 236, 246 directly toward a light combiner 250,without the use of other elements to redirect the light beamssignificantly reduces cost, complexity, and size relative to other colormanagement systems. Finally, the color management system may include aprojection lens 270 for projecting an output light beam containingspatial information for projecting an image.

In an exemplary embodiment, as shown in FIG. 4, color management system400 may comprise a third image assimilator 480 in addition to firstimage assimilator 430 and second image assimilator 440. In accordancewith this embodiment, first image assimilator 430, which comprises greenspatial light modulator 434, is positioned to receive first light beam422. Second image assimilator 440, which comprises red microdisplay 444,is positioned to receive second light beam 424. Third image assimilator480, which comprises blue panel 484, is positioned to receive thirdlight beam 426. Each image assimilator 430, 440, and 480 is configuredto modify the polarization of the incoming light beam in a predeterminedmanner and to superimpose spatial information on the light beam so as toproduce a light beam that comprises spatial information. Each such imageassimilator 430, 440, and 480 is configured for substantiallytransmitting an incoming light beam to be received by a display panel434, 444, and 484 for receiving a modified light beam from the displaypanel, and for emitting the modified light beam 436, 446, and 486 to bereceived directly by an analyzer 435, 445, 485.

In accordance with this exemplary embodiment, first image assimilator430 receives a first light beam 422, rotates its polarizationorientation, imparts first spatial information on it, and emits a firstmodified light beam 436 comprising first spatial information and noise.In addition, first image assimilator may comprise means for eliminatingor reducing waste light, and associated heat, as light is removed fromfirst light beam 422 to create first modified light beam 436. Secondimage assimilator 440 receives second light beam 424, rotates itspolarization orientation, imparts second spatial information on it, andemits a second modified light beam 446 comprising second spatialinformation and noise. In addition, second image assimilator maycomprise means for eliminating or reducing waste light, and associatedheat, as light is removed from second light beam 424 to create secondmodified light beam 446. Third image assimilator 480 receives thirdlight beam 484, rotates its polarization orientation, imparts thirdspatial information on it, and emits a third modified light beam 486comprising third spatial information and noise. In addition, third imageassimilator may comprise means for eliminating or reducing waste light,and associated heat, as light is removed from third light beam 484 tocreate third modified light beam 486. In accordance with thisembodiment, first, second, and third spatial information comprisepolarized light. It should be noted that the above described means foreliminating or reducing waste light and associated heat may be inherentin a panel (e.g., a reflective/absorptive panel) or may comprise aseparate optical element such as a polarizing beamsplitter configuredfor separating and eliminating or reducing waste light.

Accordingly, in this exemplary embodiment, the contrast of the image maybe enhanced by such analyzers 435, 445, and 485 positioned to receivethe modified light outputs from image assimilators 430, 440, and 480 andto further modify the light to produce polarized light oriented in asingle plane (i.e., substantially linearly polarized light) which may beaccomplished by rotating the polarization axis of one or more of thelight beams. Also, as mentioned in connection with the description ofanother exemplary embodiment, analyzers 435, 445, and 485 may beconfigured for removing light of a predetermined wavelength from thelight beam, depending on the characteristics of the filters (i.e., thecolor selective retardation elements).

As one skilled in the art will appreciate, a variety of configurationsmay be constructed to effectively separate an input light beamcomprising white light into a plurality of component light beams, uponwhich spatial information may be imparted, and from which noise may beeffectively separated and removed by passing such modified componentlight beams from the image assimilators to be directly received by aplurality of corresponding analyzers. Such configurations may comprise acombination of polarizing beamsplitters, mirrors, and/or field lensesarranged to separate input light into component light beams and todirect those component light beams so that they may be received byassociated image assimilators. For example, as shown in FIG. 4, in anexemplary embodiment, an input light beam 410 may be received by a firstlens 491, which transmits a light beam to be received by dichroicbeamsplitter 492. Dichroic beamsplitter transmits first component 422and second component 424, but reflects third component 426. Lens 493 ispositioned to receive reflected component 426 and to transmit component426 to be received by mirror 494. Mirror 494 is positioned to receivecomponent 426 from lens 493 and to reflect component 426 to be receivedby lens 495. Lens 495 is positioned to receive component 426 from mirror494 and to transmit component 426 to be received by image assimilator480. With further reference to FIG. 4, dichroic beamsplitter 496 ispositioned to receive components 422 and 424 from dichroic beamsplitter492 and is configured to reflect component 422 to be received by imageassimilator 430 while transmitting component 424 to be received by imageassimilator 440. Finally, it should be noted that light emitted fromimage assimilators 430, 440 may be recombined using a variety ofmechanisms known in the art, e.g., one or more Philips prism, modifiedPhilips prism, plumbicon prism, x-prism, three-channel prism,recombining prism, and the like. For example, as shown in FIG. 4, lightemitted from image assimilators 430, 440 may be recombined using anx-prism.

The invention may also include any suitable system or method forisolating stray light that may otherwise be received by an opticalcomponent of the system and combined with the desirable light beam beingtransmitted by the system. In addition, where the system includes microdisplay comprising a transmissive panel, the invention includes anysuitable system or method for rejecting waste light prior to emission ofa modified light beam from the image assimilator. For example, in anexemplary embodiment as shown in FIG. 5, color management system 500includes a light separator 596, a first image assimilator 530, a secondimage assimilator 540, and a third image assimilator 580. In addition,color management system 500 further includes a first analyzer 535positioned to receive a modified light beam directly from first imageassimilator 530, a second analyzer 545 positioned to receive a modifiedlight beam directly from second image assimilator 540, a third analyzer585 positioned to receive a modified light beam directly from thirdimage assimilator 580, and light combiner 550 positioned to receive afiltered light beams from analyzers 535, 545, 585. In accordance withthis embodiment, light separator 596 receives a light beam 510 from asource, separates the light beam 510 into two or more components, andemits two or more light beams 522, 524, each comprising one or morecomponents. Separately a third light beam 526 may be produced from asecond source or alternatively may further be separated from either oflight beams 510, 522, or 524.

With further reference to FIG. 5, first image assimilator 530, whichcomprises first transmissive panel 534, is positioned to receive firstoutput light beam 522. A second image assimilator 540, which comprisessecond transmissive panel 544, is positioned to receive second lightbeam 524. Further, a third image assimilator 580, which comprises thirdtransmissive panel 584, is positioned to receive third output light beam526. Transmissive panel is any hardware and/or software suitablyconfigured to transmit substantially all of the incipient light itreceives, but impart spatial information by spatially modifying selectedproperties (e.g., polarization) of the light beam. Each such imageassimilator 530, 540, 580 may comprise a transmissive spatial lightmodulator 534, 544, 584 configured to modify the polarization of theincoming light beam in a predetermined manner and to superimpose spatialinformation on the light beam so as to produce a light beam thatcomprises spatial information. It should be noted that such spatialinformation may comprise selectively modulated polarization ofindividual regions (i.e., pixels) selected for their spatial orientationon a display. Each such image assimilator 530, 540, 580 is configuredfor receiving an incoming light beam to be received by transmissivedisplay panel 534, 544, 584, respectively, and for emitting modifiedlight beam 536, 546, 586. In accordance with this exemplary embodiment,image assimilators 530, 540, 580 may further comprise waste lightseparators 539, 549, 589, respectively. Separators 539, 549, 589 arepositioned to receive modified light beams 536, 546, 586, respectively,to reflect useful light beams 537, 547, 587, which are to be received byanalyzers 535, 545, 585. In addition, separators 539, 549, 589 areconfigured to separate waste light components 538, 548, 588 frommodified light beams 536, 546, 586, respectively, and to reject suchwaste light. In an exemplary embodiment waste light separators 539, 549,589 may comprise a wire grid polarizer or any other such light separatorconfigured for separating useful light from waste light on the basis ofoptical properties which are modulated by the individual spatiallydistinct elements (i.e., pixels) of the transmissive panels 534, 544,584. As a result, because the waste light has been effectively separatedand eliminated thermal loading imposed upon analyzers 535, 545, 585and/or image or light recombiner 550 may be significantly reduced.

In an exemplary embodiment, color management system 500 may also beconfigured to emit output light beam 555 to be received by a projectionlens or another optical element 599. In an exemplary embodiment, opticalisolator 598 may be positioned to receive output light beam 555 prior toreceipt of light 555 by projection lens or another optical element 599.Optical isolator may be any hardware and/or software configured torotate the polarization axis of the light. In accordance with thisembodiment, stray light 597 which may be reflected by optical element599 back toward system 500 and/or combiner 550 (i.e., retroreflected)and which might otherwise be received by image recombiner 550 andtherefore recombined with output light 555, thereby producing a ghostimage. In this embodiment, optical isolator 598 is configured to rotatethe polarization axis of the light that it transmits by approximately 45degrees. As a result, the polarization axis of output light beam 555will be rotated 45 degrees as it passes through optical isolator 598producing rotated output light beam 556. As rotated output light beam556 is received by projection lens 599, and as stray light beam 591 isreflected toward optical isolator 598, with the same polarizationorientation as rotated output light beam 556. After stray light beam 591is received by optical isolator 598, however, and its polarization isrotated another 45 degrees, stray light beam 592 will have apolarization orientation that is rotated substantially 90 degrees fromthat of output light beam 555. As a result, the polarization orientationof the retroreflected light will have been rotated 90 degrees and maytherefore be separate by analyzers 535, 545, 585 or another suitablyconfigured and positioned optical component. Accordingly, the ghostimage reflected by the downstream component will have been removed orotherwise rendered substantially or fully incapable of affecting theproduction of the desired image. It should be noted that opticalisolator 598 may comprise a quarter wave retarder configured to rotatethe polarization axis of an incipient light beam by approximately 45degrees.

With reference to FIG. 3, in accordance with an exemplary embodiment ofthe present invention, a method for providing color management for aprojection system is provided comprising the steps of receiving two ormore input light beams having spatial information and noise directlyfrom associated image assimilators (step 320), separating the noise fromthe spatial information in each of the light beams (step 330), andemitting filtered light outputs comprising the spatial information (step340), whereby the output light beams have an improved contrast relativeto the input light beams.

Accordingly, the use of closely-coupled analyzers positioned to receivelight beams directly from associated image assimilators enables thecolor management system to effectively eliminate a substantial portionof noise imparted on the light beam by each of the image assimilatorsand to produce output beams having superior contrast relative to theprior art. Moreover, it should be noted that the present invention mayemploy both polarization dependent elements and dichroic elements tosplit an input light into a plurality of color bands upon which spatialinformation may be superimposed by a corresponding plurality ofmicrodisplays, the modified color bands being recombined to produce ahigh-contrast, full color projected image. One skilled in the art willappreciate that the color management system of the present invention maybe adapted for use in multiple panel systems, such as three panelsystems as well as the two panel systems primarily described herein.

Accordingly, the present invention utilizes both polarization dependentelements and dichroic elements to split (step 310) an input light into aplurality of color bands upon which spatial information may besuperimposed (step 315) by a corresponding plurality of microdisplays,the modified color bands being filtered to remove noise from the spatialinformation (step 330) and thereby improve contrast, the high contrastlight beams being thereafter recombined (step 350) to produce a fullcolor projected image.

In an exemplary embodiment, after the step of superimposing spatialinformation (step 315), and before the step of removing noise from thespatial information (step 330), it may be desirable to perform the stepof modifying the geometry of the beam (step 328) emitted from thereflective panel so as to create converging conical light beam (e.g.,rather than a more common telecentric light beam). In accordance withembodiments employing or otherwise facilitating this step, the lightbeam may be received by a downstream component (e.g., an analyzer)having a reduced cross-sectional area.

The present invention has been described above with reference to variousexemplary embodiments. However, those skilled in the art will recognizethat changes and modifications may be made to the exemplary embodimentswithout departing from the scope of the present invention. For example,the various elements may be implemented in alternate ways, such as, forexample, by providing other optical configurations or arrangements.These alternatives can be suitably selected depending upon theparticular application or in consideration of any number of factorsassociated with the operation of the system. Moreover, these and otherchanges or modifications are intended to be included within the scope ofthe present invention, as expressed in the following claims.

1. An image display device, comprising: a first panel positioned toreceive a first light beam and configured to emit a first modified lightbeam; a first wire grid polarizer positioned to receive the firstmodified light beam and configured to reflect the first filtered lightbeam; a second panel positioned to receive a second light beam andconfigured to emit a second modified light beam; a second wire gridpolarizer positioned to receive the second modified light beam andconfigured to reflect the second filtered light beam; and a lightcombiner for combining the first filtered light beam and the secondfiltered light beam to produce a substantially linearly polarized lightbeam.
 2. The image display device of claim 1, further comprising a lightseparator for separating light into the first light beam and the secondlight beam, wherein the light separator is distinct from the lightcombiner.
 3. The image display device of claim 1, further comprising afirst filter positioned between the first wire grid polarizer and thelight combiner.
 4. The image display device of claim 1, furthercomprising a second filter positioned between the second wire gridpolarizer and the light combiner.
 5. The image display device of claim1, further comprising an optical isolator configured to receive thesubstantially linearly polarized light beam.
 6. The image display deviceof claim 1, wherein the first modified light beam includes first spatialinformation and the second modified light beam includes second spatialinformation.
 7. The image display device of claim 1, further comprising:a third panel positioned to receive a third light beam and configured toemit a third modified light beam; a third wire grid polarizer positionedto receive the third modified light beam and configured to reflect thethird filtered light beam; and a light combiner for combining the firstfiltered light beam, the second filtered light beam and the thirdfiltered light beam to produce a substantially linearly polarized lightbeam.
 8. An image display device, comprising: a separator for separatinglight into a first light beam and a second light beam; a firstmicrodisplay positioned to receive the first light beam and configuredto impart spatial information on the first light beam to produce amodified first light beam; a second microdisplay positioned to receivethe second light beam and configured to impart spatial information onthe second light beam to produce a modified second light beam; one ormore beamsplitters positioned to receive the modified first light beamand the modified second light beam; a combiner, spaced apart from theseparator, positioned to receive the modified first light beam and themodified second light beam and configured to emit a substantiallylinearly polarized light beam; an optical isolator configured to receivethe substantially linearly polarized light beam; and wherein the firstand second microdisplays are transmissive panels.